Pigment dispersion and ink composition for ink-jet

ABSTRACT

An aqueous pigment dispersion for ink jet having a pigment dispersed, characterized by containing a water-soluble resin and a resin having a urethane bond and/or an amide bond.

TECHNICAL FIELD

[0001] The present invention relates to a pigment dispersion suitablyusable for various ink compositions including use for ink jet printing,and an ink for ink jet printing.

BACKGROUND ART

[0002] A pigment type ink using a pigment as a coloring agent has anadvantage of being excellent in light resistance and water resistance ascompared with a dye type ink using a dye as a coloring agent. However,since a pigment is generally insoluble in water, it is necessary to bemixed with a resin called as a dispersant for being stably dispersed inwater. Also, as compared with a dye type ink, a pigment type ink as adispersion is poor in stability as a lapse of time since a pigmentsettles.

[0003] Also, it is pointed out that a pigment type ink generally has adisadvantage of being poor in transparency and coloring. Particularly,when recording on a transmission manuscript represented as an OHP filmprocessed for an aqueous recording liquid, transparency is lowered andcoloring is remarkably dull due to light scattering by pigmentparticles.

[0004] It is required for ink jet use to be printed at a high speed, butunlike a dye penetrated into the inside of a recording medium, a pigmentstays on a surface of a recording medium and accordingly frictionresistance of an image obtained becomes a problem.

[0005] In order to improve transparency and coloring, it is necessary tohave pigment particles dispersed as finely as possible. Particularly, incase of ink jet use for injecting ink droplets from a minute nozzle, astrict dispersion stability and a highly finely dispersed state arerequired in order to achieve satisfactory performances such as colorreproducibility on a recorded material and injecting property at thetime of injecting from a nozzle at a high speed. For this purpose,various elaborations are made. For example, an elaboration of fullyadsorbing a high molecular dispersant on a pigment or an elaboration offirmly fixing a high molecular dispersant on a finely dispersed pigmentby means of coating a pigment with a resin is studied.

[0006] For instance, the following proposals have been made. A pigmentand a resin are kneaded to prepare a solid colored compound, and thecompound is dispersed in a dispersing medium to improve transparency andcoloring (JP-A-11-80,633); a storage stability of a dispersion isimproved by using a pigment coated with a cured polymer having a polargroup insoluble in a dispersion medium (JP-A-5-247,370); a pigment iscoated with a resin swellable in a dispersion medium to prevent cloggingor bleeding (JP-A-3-240,586); and an aqueous solution containing aresin, an amine and water are stirred to fully dissolve the resin, and apremixed pigment is subjected to dispersion treatment to stabilizeinjecting by controlling a non-adsorbed resin amount to at most 2%(JP-A-2-255,875).

[0007] In the ink jet use, it is required for improving a printing speedto enhance permeability of an ink composition and to reduce a dryingtime. However, when simply adding a general penetrant, there is a casethat the permeability can not be fully provided due to a relationshipbetween a pigment and other components or a case that the penetrantdamages color reproducibility, which adversely affects on an imagequality. Therefore, various proposals have been made to solve theseproblems.

[0008] For example, by using an acetylene glycol type and/orpolysiloxane type surfactant as a penetrant and using an alkyl etherderivative of a polyhydric alcohol such as ethylene glycol monobutylether as an organic solvent, a satisfactory color reproducibility isachieved (JP-A-2002-30,237); and by using an ink containing water, apigment, a wetting agent and a specific polyoxyethylene alkyl etheracetate, an ink having excellent permeability, drying property and imagequality and having no strike through is provided (JP-A-2001-254,036).

[0009] However, when preparing an ink having a high permeability and aquick drying property, it has been found by the present inventors that astable dispersibility of a pigment is sometimes spoiled by aninteraction among a dispersing resin, a penetrant and a solvent forpreparing the ink.

[0010] The present inventors have intensive studied to solve theseproblems. As a result of the study, it has been found that an excellentink for ink jet and an excellent pigment dispersion for ink jet having asatisfactory dispersion stability can be obtained without spoiling otherperformances by using a dispersion having a combination of specificplural resins contained, particularly in the preparation of an inkhaving a high permeability.

[0011] Further, it has been unexpectedly discovered that gloss of arecorded material is improved by the present invention as compared witha conventional pigment type ink. Particularly, it has been found thatwhen using a glossy paper as a medium, the improvement of gloss isremarkable.

DISCLOSURE OF THE INVENTION

[0012] Thus, the essential features of the present invention reside in:

[0013] (1) A pigment dispersion for ink jet having a pigment dispersed,characterized by containing a water-soluble resin and a resin having aurethane bond and/or an amide bond;

[0014] (2) the pigment dispersion according to the above feature (1),which is obtained by blending the water-soluble resin with the pigment,finely pulverizing the pigment in a kneading step and a dispersing step,and further adding the resin having a urethane bond and/or an amide bondthereto to cause crosslinking;

[0015] (3) the pigment dispersion according to the above feature (1) or(2), wherein the resin has a crosslinking rate of from 20 to 100%;

[0016] (4) the pigment dispersion according to any one of the abovefeatures (1) to (3), which is a dispersion for ink jet;

[0017] (5) an ink composition for ink jet having a pigment dispersed,characterized by containing a water-soluble resin and a resin having aurethane bond and/or an amide bond;

[0018] (6) the ink composition for ink jet according to the abovefeature (5), which is obtained by blending the water-soluble resin withthe pigment, finely pulverizing the pigment in a kneading step and adispersing step, and further adding the resin having a urethane bondand/or an amide bond thereto to cause crosslinking;

[0019] (7) the ink composition for ink jet according to the abovefeature (5) or (6), wherein the resin has a crosslinking rate of from 20to 100%;

[0020] (8) an ink composition for ink jet, which is obtained by addingan organic solvent to the pigment dispersion as defined in any one ofthe above features (1) to (3);

[0021] (9) an ink jet recording method, which comprises printing bydischarging the ink composition for ink jet as defined in any one of theabove features (5) to (8) from a nozzle of an ink jet printer; and

[0022] (10) an ink set having the ink composition for ink jet as definedin any one of the above features (5) to (8) charged into a cartridge.

[0023] Hereinafter, the present invention is described in details. Thepigment dispersion of the present invention comprises at least a pigmentand specific two kinds of resins.

[0024] (Pigment)

[0025] The pigment used in an aqueous ink composition for ink jet of thepresent invention is not specifically limited, and any of an organicpigment and an inorganic pigment can be used.

[0026] Examples of the organic pigment include an azo pigment such as anazolake, an insoluble monoazo pigment, an insoluble disazo pigment, acondensed azo pigment, a chelate azo pigment or the like; a polycyclicpigment such as a phthalocyanine pigment, a perylene pigment, a perynonepigment, an anthraquinone pigment, a quinacridone pigment, a dioxazinepigment, a thioindigo pigment, an isoindolinone pigment, aquinophthalone pigment or the like; a dye chelate such as a basic dyetype chelate, an acidic dye type chelate or the like; a nitro pigment; anitroso pigment; and the like.

[0027] Examples of the inorganic pigment include titanium oxide, ironoxide, rouge, chromium oxide, Prussian blue, ultramarine blue, molybdateorange, black iron oxide, chrome yellow, carbon black, and the like, andthey can be used respectively alone or in a mixture of two or more.

[0028] Among them, in view of light resistance, an isoindolinone typepigment, a quinacridone type pigment, a condensed azo type pigment, aphthalocyanine type pigment, a quinophthalone type pigment, ananthraquinone type pigment or carbon black is preferably usable.

[0029] Particular examples of the above organic pigments includepigment•yellow 1 (color index (hereinafter referred to as “C.I.”)11680), pigment•yellow 3 (C.I. 11710), pigment•yellow 14 (C.I. 21095),pigment•yellow 17 (C.I. 21105), pigment•yellow 42 (C.I. 77492),pigment•yellow 74 (C.I. 11741), pigment•yellow 83 (C.I. 21108),pigment•yellow 93 (C.I. 20710), pigment•yellow 98 (C.I. 11727),pigment•yellow 109 (C.I. 56284), pigment•yellow 110 (C.I. 56280),pigment•yellow 128 (C.I. 20037), pigment•yellow 138 (C.I. 56300),pigment•yellow 139 (C.I. 56298), pigment•yellow 147 (C.I. 60645),pigment•yellow 154 (C.I. 11781), pigment•yellow 155, pigment•yellow 180(C.I. 21290), pigment•yellow 185, pigment•orange 5 (C.I. 12075),pigment•orange 13 (C.I. 21110), pigment•orange 16 (C.I. 21160),pigment•orange 34 (C.I. 21160), pigment•orange 43 (C.I. 71105),pigment•orange 61 (C.I. 11265), pigment•orange 71 (C.I. 561200),pigment•red 5 (C.I. 12490), pigment•red 8 (C.I. 12335), pigment•red 17(C.I. 12390), pigment•red 22 (C.I. 12315), pigment•red 48:2 (C.I.15865:2), pigment•red 112 (C.I. 12370), pigment•red 122 (C.I. 73915),pigment•red 177 (C.I. 65300), pigment•red 178 (C.I. 71155), pigment•red202 (C.I. 73907), pigment•red 254 (C.I. 56110), pigment•red 19 (C.I.46500), pigment•violet 23 (C.I. 51319), pigment•blue 15:1 (C.I. 74160),pigment•blue 15:3 (C.I. 74160), pigment•blue 15:4 (C.I. 74160),pigment•blue 60 (C.I. 69800), pigment•green 7 (C.I. 74260),pigment•green 36 (C.I. 74265), and the like.

[0030] Particular examples of the above inorganic pigments includepigment•yellow 42 (C.I. 77492), pigment-white 6 (C.I. 77891),pigment•blue 27 (C.I. 77510), pigment•blue 29 (C.I. 77007),pigment•black 7 (C.I. 77266), and the like.

[0031] Preferable examples include pigment•yellow 74 (C.I. 11741),pigment•yellow 109 (C.I. 56284), pigment•yellow 110 (C.I. 56280),pigment•yellow 128 (C.I. 20037), pigment•yellow 155, pigment•yellow 180(C.I. 21290), pigment•red 122 (C.I. 73915), pigment•red 202 (C.I.73907), pigment•violet 19 (C.I. 46500), pigment•blue 15:1 (C.I. 74160),pigment•blue 15:3 (C.I. 74160), pigment•blue 15:4 (C.I. 74160),pigment•blue 60 (C.I. 69800), pigment•black 7 (C.I. 77266), and thelike.

[0032] In the present invention, it is preferable to use an organicpigment in view of stability since its particle size easily becomessmall and its specific gravity is also small. Further, when consideringdispersibility, a primary particle size of a pigment is preferably atmost about 0.1 μm.

[0033] (Water-Soluble Resin)

[0034] The present invention is characterized by including at least twokinds of resins.

[0035] First resin is a water-soluble resin including various resinsusable as a dispersant which is adsorbed on a pigment and works forimproving dispersibility of the pigment.

[0036] Among them, a water-soluble resin having a hydrophobic group anda hydrophilic group is desirable since it is excellent in dispersing apigment. Typical examples include a copolymer of a hydrophobic monomerand a hydrophilic monomer, and such a copolymer is particularlyexcellent in dispersing a pigment.

[0037] The term “hydrophobic monomer” means a monomer having ahydrophobic group and the term “hydrophilic monomer” means a monomerhaving a hydrophilic group, which are copolymerizable.

[0038] Examples of the hydrophobic monomer include methyl acrylate,methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propylacrylate, n-propyl methacrylate, iso-propyl acrylate, iso-propylmethacrylate, n-butyl acrylate, n-butyl methacrylate, sec-butylacrylate, sec-butyl methacrylate, tert-butyl acrylate, tert-butylmethacrylate, n-hexyl acrylate, n-hexyl methacrylate, n-octyl acrylate,n-octyl methacrylate, iso-octyl acrylate, iso-octyl methacrylate,2-ethylhexyl acrylate, 2-methylhexyl methacrylate, decyl acrylate, decylmethacrylate, lauryl acrylate, lauryl methacrylate, stearyl acrylate,stearyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxyethylmethacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate,2-dimethylaminoethyl acrylate, 2-dimethylaminoethyl methacrylate,2-diethylaminoethyl acrylate, 2-diethylaminoethyl methacrylate, glycidylacrylate, glycidyl methacrylate, allyl acrylate, allyl methacrylate,cyclohexyl acrylate, cyclohexyl methacrylate, phenyl acrylate, phenylmethacrylate, nonylphenyl acrylate, nonylphenyl methacrylate, benzylacrylate, benzyl methacrylate, dicyclopentenyl acrylate, dicyclopentenylmethacrylate, bornyl acrylate, bornyl methacrylate, 1,3-butanedioldiacrylate, 1,3-butanediol dimethacrylate, 1,4-butanediol diacrylate,1,4-butanediol dimethacrylate, ethylene glycol diacrylate, ethyleneglycol dimethacrylate, diethylene glycol diacrylate, diethylene glycoldimethacrylate, triethylene glycol diacrylate, triethylene glycoldimethacrylate, tetraethylene glycol diacrylate, tetraethylene glycoldimethacrylate, polyethylene glycol diacrylate, polyethylene glycoldimethacrylate, neopentyl glycol diacrylate, 1,6-hexanediol diacrylate,1,6-hexanediol dimethacrylate, dipropylene glycol diacrylate,dipropylene glycol dimethacrylate, trimethylolpropane triacrylate,trimethylolpropane trimethacrylate, glycerol acrylate, glycerolmethacrylate, styrene, methylstyrene, vinyl toluene, and the like.

[0039] They may be used respectively alone or in a mixture of two ormore.

[0040] A hydrophobic group contained in a hydrophobic monomer is notspecially limited, examples of which include an organic group having anaromatic ring such as a phenyl group, a benzyl group or the like, whichmay be substituted, and an alkyl group which may be substituted, but aring having an aromatic ring is particularly preferable.

[0041] Examples of a hydrophilic monomer include acrylic acid,methacrylic acid, maleic acid, itaconic acid and the like.

[0042] They may be used respectively alone or in a mixture of two ormore. A ratio of a hydrophilic monomer and a hydrophobic monomer is notspecially limited, but it is particularly preferable that a hydrophilicmonomer: hydrophobic monomer weight ratio is in a range of from 5:95 to40:60.

[0043] A copolymer can be obtained by copolymerizing these hydrophobicmonomers and hydrophilic monomers. Polymerization can be carried out bya known method, but it is preferable that copolymerization is carriedout by a random copolymerization method since a copolymer obtained byrandom copolymerization provides an excellent stability as a lapse oftime when a dispersion is prepared by using the copolymer thus obtainedas a dispersant.

[0044] It is particularly preferable to use an alkali-soluble resinobtained by neutralizing the above-mentioned copolymer of a hydrophobicmonomer and a hydrophilic monomer with an alkaline material as aneutralizer to have the polymer solubilized in an aqueous medium.

[0045] Examples of the neutralizer include an alkali metal hydroxidesuch as sodium hydroxide, potassium hydroxide or the like,monoethanolamine, diethanolamine, triethanolamine, monoethylamine,diethylamine, triethylamine, morpholine, ammonia, and the like.

[0046] Preferable examples of the water-soluble resin having ahydrophilic group and a hydrophobic group include a styrene-acrylic acidcopolymer, a styrene-methylstyrene-acrylic acid copolymer, astyrene-acrylic acid-(meth)acrylic acid ester (a lower alkyl ester ofabout C₁C₄, hereinafter the same) copolymer, a methacrylicacid-(meth)acrylic acid ester copolymer, an acrylic acid-(meth)acrylicacid ester copolymer, a styrene-methacrylic acid copolymer, astyrene-maleic acid copolymer, a styrene-methylstyrene-maleic acidcopolymer, a styrene-(meth)acrylic acid ester-maleic acid copolymer, astyrene-(meth)acrylic acid ester-allylsulfonic acid copolymer, avinylnaphthalene-acrylic acid copolymer, a vinylnaphthalene-maleic acidcopolymer, or their sodium, potassium or ammonium salts, and the like.They may be used respectively alone or in a mixture of two or more.

[0047] Among them, particularly preferable examples include astyrene-acrylic acid copolymer, a styrene-methylstyrene-acrylic acidcopolymer, a styrene-maleic acid copolymer, a methacrylicacid-(meth)acrylic acid ester copolymer, and the like. When they areused, a pigment dispersion having particularly excellent dispersibilitycan be obtained.

[0048] Other various water-soluble resins known as a high moleculardispersant can also be used. For example, a polyvinyl alcohol typedispersant, a polyacrylamide type dispersant, a polyester typedispersant, a polyacrylic acid type dispersant or the like is known, andthey may be selected from commercially available products.

[0049] A glass transition point of the water-soluble resin is notspecially limited, but a preferable glass transition point is at least30° C., more preferably at least 50° C. When the glass transition pointis less than 30° C., a dispersion and an ink composition become poor instability as a lapse of time. When the glass transition point is lessthan 30° C., a pigment having a function partially as a dispersant doesnot work when a temperature is raised, and consequently the stability asa lapse of time becomes poor.

[0050] The glass transition point indicates a temperature zone whereinphysical properties rapidly vary by partial crystallization or hydrogenbonding in the inside of a non-crystalline solid such as a plastic whena temperature is lowered, and can be measured by a thermally analyzingapparatus such as “DSC7” of Perkin Elmer Co. It is general to carry outthe thermal analysis at a temperature gradient of 5 to 10° C./min.

[0051] Particularly, a copolymer comprising a hydrophobic monomer suchas styrene or (meth)acrylic acid ester and a hydrophilic monomer such as(meth)acrylic acid, and having a glass transition point of at least 30°C., more preferably at least 50° C., is particularly excellent indispersion stability.

[0052] A molecular weight of a water-soluble resin is not speciallylimited, but a preferable molecular weight is 2,000 to 30,000, morepreferably 2,000 to 20,000, as a weight average molecular weightmeasured by GPC (gel permeation chromatography).

[0053] Also, an acid value of a water-soluble resin is preferably from50 to 320, more preferably from 55 to 270. The acid value is an mgamount of KOH necessary for neutralizing 1 g of a resin.

[0054] A water-soluble resin is added in an amount of from 5 to 100parts by weight, more preferably from 10 to 80 parts by weight, to 100parts by weight of a pigment. If the amount of a water-soluble resin isless than 5 parts by weight to 100 parts by weight of a pigment,dispersibility of a pigment becomes insufficient and a deposit is formedor a stability as a lapse of time becomes poor. On the other hand, ifthe amount of a water-soluble resin exceeds 100 parts by weight, adispersion or an ink prepared therefrom becomes highly viscous, and aninjecting performance is lowered.

[0055] (Resin Having an Amide Bond and/or A Urethane Bond)

[0056] The present invention further employs a resin having an amidebond and/or a urethane bond as a second resin in addition to theabove-mentioned water-soluble resins. Their examples include ahomopolymer obtained by polymerizing (meth)acrylamide, vinylpyrrolidoneor the like, a copolymer of the above illustrated homopolymers withother vinyl monomers, a polyurethane resin, and the like.

[0057] Among them, a polyurethane resin is particularly preferable. Thepolyurethane resin is not specially limited, and a water-soluble orwater-dispersible polyurethane resin obtained by reacting a diisocyanatecompound and a diol compound is usable.

[0058] Examples of the diisocyanate compound include an alicyclicdiisocyanate compound such as hexamethylene diisocyanate,2,2,4-trimethylhexamethylene diisocyanate, hydrogenated xylylenediisocyanate, 1,4-cyclohexane diisocyanate, 4,4′-dicyclohexylmethanediisocyanate or the like, an arylaliphatic diisocyanate compound such asxylylene diisocyanate, tetramethylxylylene diisocyanate or the like, anaromatic diisocyanate compound such as toluilene diisocyanate,phenylmethane diisocyanate or the like, a modified material of the aboveillustrated diisocyanates (such as carbodiimide, uretodion oruretoimine-containing modified materials), and the like.

[0059] Examples of the diol compound include a diol compound obtained by(co)polymerizing an alkylene oxide such as ethylene oxide or propyleneoxide, and a heterocyclic ether such as tetrahydrofuran or the like.Particular examples of the diol compound include a polyether diol suchas polyethylene glycol, polypropylene glycol, polytetramethylene etherglycol, polyhexamethylene ether glycol or the like, a polyester diolsuch as polyethylene adipate, polybutylene adipate, polyneopentyladipate, poly-3-methylpentyl adipate, polyethylene/butylene adipate,polyneopentyl/hexyl adipate or the like, a polylactone diol such aspolycaprolactone diol or the like, polycarbonate diol, and the like.Among them, at least one kind of polyether type, polyester type andpolycarbonate type diol compounds is preferable.

[0060] Further, in addition to the above compounds, diol compoundshaving an acidic group such as a carboxylic acid group, a sulfonic acidgroup or the like are usable, examples of which include dimethylolaceticacid, dimethylolpropionic acid, dimethylolbutyric acid and the like.Among them, dimethylolpropionic acid is preferable.

[0061] These diol compounds may be used in a combination of two or morekinds.

[0062] In the preparation of a polyurethane type resin, a polyhydroxycompound having a low molecular weight may be added. Examples of thepolyhydroxy compound having a low molecular weight includes a materialusable as a starting material for polyester diol, such as glycol, analkylene oxide low mol adduct, a trihydric alcohol such as glycerin,trimethylolethane or trimethylolpropane, and their alkylene oxide lowmol adducts. Also, with regard to the urethane prepolyemr thus obtained,a chain can be extended after neutralizing or during neutralizing anacid group derived from dimethylolalkanoic acid or a chain can beextended with di(tri)amine. Examples of a polyamine used in theextension of chain include hexamethylenediamine, isophoronediamine,hydrazine, piperazine or the like, and they may be used in a combinationof two or more.

[0063] The form of a urethane resin is not limited. Typical formsinclude an emulsion type such as self-emulsified emulsion orself-stabilized type. Particularly, among the above compounds, a diolhaving an acidic group such as a carboxylic acid group, a sulfonic acidgroup or the like is preferably usable, or a polyhydroxy compound havinga low molecular weight may be added, or a urethane resin having anacidic group introduced, particularly one having a carboxyl group, isdesirable. Further, it is preferable for improving gloss or frictionresistance to crosslink these functional groups such as a carboxyl groupwith the following crosslinking treatment.

[0064] These resins further neutralized are usable, and examples of abase used for neutralization include an alkyl amine such as butyl amineor trimethyl amine, an alkanol amine such as monoethanol amine,diethanol amine or triethanol amine, morpholine, ammonia, and aninorganic base such as sodium hydroxide or the like.

[0065] Examples of a high molecular material having an amide bond and/ora urethane bond include a polyether type polyurethane resin, a polyestertype polyurethane resin or a polycarbonate type polyurethane resin,which are obtained by using a polyether type diol, a polyester type diolor a polycarbonate type diol.

[0066] Also, an acid value of the high molecular compound having anamide bond and/or a urethane bond is not specially limited, but ispreferably from 5 to 100, more preferably from 10 to 80. Preferableexamples of the high molecular compound having an amide bond and/or aurethane bond include NeORez R-960 (manufactured by Zeneca), NeORezR-989 (manufactured by Zeneca), NeORez-9320 (manufactured by Zeneca),NeORad NR-440 (manufactured by Zeneca), Hydran AP-30 (manufactured byDainippon Ink and Chemicals, Incorporated), Hydran APX-601 (manufacturedby Dainippon Ink and Chemicals, Incorporated), Hydran SP-510(manufactured by Dainippon Ink and Chemicals, Incorporated), HydranSP-97 (manufactured by Dainippon Ink and Chemicals, Incorporated),Elastron MF-60 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.),Elastron MF-9 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), M-1064(manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Izelax S-1020(manufactured BY Hodogaya Chemical Co., Ltd.), Izelax S-1040(manufactured by Hodogaya Chemical Co., Ltd.), Izelax S-1085C(manufactured by Hodogaya Chemical Co., Ltd.), Izelax S-4040N(manufactured by Hodogaya Chemical Co., Ltd.), Neotan UE-5000(manufactured by Toagosei Co., Ltd.), RU-40 series (manufactured by StalJapan), Ucoat UWS-145 (manufactured by Sanyo Chemical Industries, Ltd.),Parmarin UA-150 (manufactured by Sanyo Chemical Industries, Ltd.), WF-41series (manufactured by Stal Japan) and WPC-101 (manufactured by NipponPolyuretahne Industry Co., Ltd.).

[0067] The resin having a urethane bond and/or an amide bond is added inan amount of from 5 to 100 parts by weight, preferably from 10 to 80parts by weight, to 100 parts by weight of a pigment. If the amount ofthe resin is less than 5 parts by weight to 100 parts by weight of apigment, friction resistance of a recorded material becomes poor, andstability as a lapse of time also becomes poor. On the other hand, ifthe amount of the resin exceeds 100 parts by weight, a dispersion and anink composition become highly viscous, and an injecting performancebecomes lowered, thereby lowering gloss.

[0068] (Resin Adsorbed to Pigment and Free Resin)

[0069] The present invention is characterized by using a combination ofthe above-mentioned water-soluble resin and the resin having an amidebond and/or a urethane bond. An adding method is not limited, butpreferably the water-soluble resin is first added to a pigment.Thereafter, the mixture is subjected to the following kneading step toform a dispersion having the pigment dispersed therein, and then it ispreferable to add the resin having an amide bond and/or a urethane bondto the dispersion. It is preferable to carry out the followingcrosslinking treatment before or after adding the resin having an amidebond and/or a urethane bond. Particularly, it is preferable to carry outthe crosslinking treatment after adding the resin having an amide bondand/or a urethane bond. It has been found that dispersion stability andgloss are remarkably improved by adding the resins in this manner. Thisis probably because the water-soluble resin is firmly fixed onto thepigment surface in the kneading step to achieve a desired dispersionstate, and the water-soluble resin and the resin having an amide bondand/or a urethane bond forms a film coated on the pigment surface by thecrosslinking reaction, and the film is more firmly fixed and stabilized.At the same time, an amount of a free resin not adsorbed on the pigmentcan be reduced, and the added resin can effectively disperse thepigment, thereby achieving quite satisfactory dispersion stability.Also, by using a urethane resin having an acidic group introduced as theresin having an amide bond and/or a urethane bond, particularly onehaving a carboxyl group, these carboxyl groups are crosslinked with afunctional group such as a carboxyl group contained in the previouslyadded water-soluble resin by a crosslinking agent in the crosslinkingstep, thus more firmly bonding to the pigment. It is more preferable tocarry out the crosslinking treatment after adding the resin having anamide bond and/or a urethane bond, but even before adding the resinhaving an amide bond and/or a urethane bond, the crosslinking treatmentmay be carried out after adding the water-soluble resin and thecrosslinked water-soluble resin is firmly fixed on the pigment toimprove stability.

[0070] For example, this is proved by measuring a ratio of a resinadsorbed on a pigment and other unadsorbed free resin by the followingmethod. The method for measuring an amount of an unadsorbed resincomprises precipitating a pigment and a resin content adsorbed on thepigment by an ultra-centrifugal machine, and then measuring an amount ofa remaining resin contained in the supernatant liquid by TOC (totalorganic carbon meter) or gravimetric method (method comprisingevaporating the supernatant liquid to solid and measuring a resinamount) (JP-A-2-255,875).

[0071] A particularly suitable method in the present invention comprisessubjecting a liquid to an ultra-high speed cooling centrifugal machine(Beckman-made) at 55,000 rpm for 5 hours to precipitate a pigmentcontent and a resin content adsorbed on the pigment, thereafter taking apredetermined amount of the supernatant liquid or taking only a resinnot adsorbed by a membrane-separating method such as an ultrafiltrationmethod, and then drying to solid by a vacuum dryer (60° C., 24 hours).This resin amount is calculated by percentage as a remaining resinconcentration to the charged ink.

[0072] Firstly, a satisfactory dispersion can be achieved by dispersinga pigment at a stage of adding a water-soluble resin, and then a resinhaving an amide bond and/or a urethane bond is added to carry outcrosslinking treatment, thereby firmly fixing the both resins to thepigment. Further, when a solvent having a high permeability is addedthereto, stability is improved and agglomeration of pigments at the timeof drying is hardly caused, and smoothness of a paper surface isimproved, thus improving gloss also.

[0073] A weight ratio of a water-soluble resin and a resin having aurethane bond and/or an amide bond is preferably (water-solubleresin)/(resin having a urethane bond and/or an amide bond)=1/2 to 2/1based on respective solid contents, and particularly when printing in aweight ratio of ranging from 1/1.5 to 1.5/1, a printed image becomesexcellent in gloss.

[0074] (Kneading Step)

[0075] In the present invention, it is preferable to first knead apigment and the above-mentioned water-soluble resin. The kneading stepis not specially limited and a well known step may be employed so longas the pigment and the water-soluble resin are kneaded in contact witheach other. A solid content ratio (weight) of pigment: water-solubleresin is preferably 95:5-65:35, more preferably 90:10-70:30. Also,depending on the state of a pigment and a water-soluble resin, a systemof being mixed with water may be employed, and in such a case, anordinary stirrer may be satisfactorily used. If necessary, a pigment maybe wetted with a water-soluble resin. Generally, a resin and awater-soluble resin, and an organic resin added optionally as desired,are charged into a kneading apparatus, and are kneaded therein.

[0076] The organic solvent used is not specially limited, but it ispreferable to use a solvent having such a high boiling point as notbeing volatilized in the kneading step in order to prevent the pigmentfrom splashing during the step, and it is preferable to have the resindissolved by using a solvent having a lower boiling point incombination.

[0077] Examples of the solvent having a high boiling point includepolyhydric alcohols such as ethylene glycol, propylene glycol,diethylene glycol, dipropylene glycol, polyethylene glycol or glycerin,pyrrolidones such as N-methyl-2-pyrrolidone or 2-pyrrolidone, and thelike. An amount of the solvent used is selected depending on acombination of a pigment and a resin in such a manner as to apply anappropriate shear to a mixture of a pigment and a resin during thekneading operation, and the solvent is generally added in an amount offrom 20 to 100 parts by weight, preferably from 30 to 80 parts byweight, to 100 parts by weight of a pigment.

[0078] Examples of the organic solvent having a low boiling point usedat the time of kneading include alcohols such as methanol, ethanol orisopropyl alcohol, and ketones such as acetone or methyl ethyl ketone.

[0079] A kneading apparatus employed is not specially limited so long asit provides an appropriate shear to a mixture of a pigment and a resinin contact with each other at the time of kneading, and may be selectedfrom general kneading apparatuses. Typical examples include two-roll orthree-roll rollers or kneaders. The mixture of a pigment and awater-soluble resin in a kneading apparatus is heated by the heat of theapparatus or self-heated by a shear force received from the kneadingapparatus, thereby raising a temperature. It is desirable that the resinbecomes a molten state at this time, and that the pigment is pulverizedby the shear force provided from the kneading apparatus and is dispersedin the resin. The kneading temperature is adjusted to be from 25 to 200°C., preferably from 100 to 150° C.

[0080] Various methods are usable as a method for preparing an inkcomposition or a pigment dispersion from the kneaded product of pigmentobtained in the above kneading step, but it is preferable to neutralizea base of the resin with alkali.

[0081] The neutralization may be carried out by adding the pigmentkneaded product to a solvent having an alkaline compound added in water,and mixing and stirring. The alkaline compound used for neutralizationis not specially limited. Examples of the alkaline compound includeorganic amines such as ammonia, monomethanol amine, diethanol amine,triethanol amine, morpholine or 2-amino-2-methyl-1-propanol; and alkalimetal salts such as sodium hydroxide, potassium hydroxide or ammoniumhydroxide.

[0082] It is most idealistic that an amount of the alkaline compoundadded is such an amount as to completely neutralize a hydrophilic groupin the resin, and accordingly it is preferable to make a neutralizationrate of 80 to 150%, particularly 90 to 120%, which is determined by anequivalent amount of the alkaline compound added and an acid equivalentamount of the resin.

[0083] It is preferable to heat the materials at the time ofneutralizing. The heating temperature is preferably from 40 to 100° C.,more preferably from 60 to 90° C.

[0084] The pigment kneaded product is dispersed by a dispersing machinesuch as a beads mill as described below. At this time, various additivessuch as a preservative, a wetting agent and the like may be added inaddition to the pigment kneaded product, water and alkali.

[0085] (Dispersing Step)

[0086] In the present invention, it is quite preferable to finelypulverize a pigment by carrying out a dispersing step after the abovekneading step. Dispersing means are not specially limited, and typicalexamples include various mechanical methods conventionally employed inthe preparation of a pigment fine particle dispersion, e.g. a mechanicalmethod such as a grinding method using a ball mill and a pulverizingmethod by vibration such as an ultrasonic dispersing machine. Further,it is well known to employ a method of using a dispersing machine calledas a sand mill, a basket mill or a pearl mill for an apparatus ofobtaining finer particles.

[0087] It is preferable in the present invention to stir the pigmentkneaded product obtained in the above kneading step with a dispersingmedium and to disperse the product by a shear force of the dispersingmedium. The dispersing medium and a dispersing machine used herein arenot specially limited, and conventionally well known various materialsmay be used. As a wet type pulverizing apparatus carrying out dispersionby pass-system or multi-system, it is particularly preferable to employan apparatus having an ability of separating a dispersing medium as finebeads having a diameter of at most 0.5 mm.

[0088] The dispersing medium is not specially limited, but itspreferable examples include ceramics; hard glass such as soda glassbeads or alkali-free beads; hard plastic beads such as polymethylmethacrylate beads; metals such as chrome beads or stainless steelbeads; or metal compounds such as zirconia. Zirconia is particularlypreferable since it can produce satisfactorily fine particles.

[0089] In order to sufficiently disperse a pigment and to make finerparticles, an amount of a dispersing medium loaded into a dispersingmachine is at least 65%, preferably at least 70%, and a mixing ratio ofa dispersing medium and an aqueous pigment composition (dispersingmedium/aqueous pigment composition (volume ratio)) is at least 1/30,preferably at least 1/25, and when considering a practical operationefficiency, the mixing ratio is preferably at most 1/1, more preferablyat most 1/2.

[0090] Further, it is preferable to operate a wet system pulverizingapparatus having the above-mentioned dispersing machine at a peripheralvelocity of at least 5 m/s, preferably at least 7 m/s, in respect ofmaking fine particles of a pigment.

[0091] Further, the time of operating the wet system pulverizingapparatus is not specially limited, but may be from about 2 to 150minutes as a residence time of dispersion.

[0092] (Dispersion State)

[0093] It is preferable that a particle size is at least 5 nm and atmost 200 nm after dispersing a pigment. Further, it is preferable tofinally make a pigment having a particle size in a range of from 5 to100 nm by removing coarse particles by centrifugal treatment. If theparticle size exceeds 100 nm, separation or settling of pigments tendsto occur. On the other hand, if the particle size is smaller than 5 nm,control or light resistance performances of particles become poor. Aparticularly preferable particle size is in a range of from 5 to 80 nm.

[0094] This particle size is a dispersed particle size (volume 50%particle size) of pigment particles actually forming a dispersion, andMicrotrac UPA (LEEDS & NORTHRUP Co.) is used as a measuring device.

[0095] (Crosslinking Treatment)

[0096] After dispersing a pigment, it is preferable to crosslink a resinadsorbed on the pigment with a crosslinking agent. A pigment is finelypulverized in a kneading step and a dispersing step, and it ispreferable to crosslink a resin in a dispersion state before or afteradding a resin having a urethane bond and/or an amide bond. Acrosslinking agent crosslinkable at a low temperature of about 0 to 100°C. is preferable as a crosslinking agent, and a crosslinking agent ofcompletely water-soluble type or organic solvent-containingwater-soluble type polymer or oligomer is preferable in respect ofproviding a uniform reaction in an aqueous dispersion, but is notlimited thereto. This crosslinking reaction is a reaction of producing anew chemical bond bonding high molecular materials having a chain-likestructure to newly develop a tridimensional net-like structure, andincludes a case of further crosslinking high molecular materials alreadyhaving a partially crosslinked structure and also a case ofprecipitating a higher molecular material from a dissolved resin. Acuring reaction is also included in the crosslinking reaction.

[0097] Examples of the crosslinking agent include a carboxylgroup-reactive type such as a polycarbodiimide type having acarbodiimide group in a molecule, an oxazoline type having an oxazolinegroup in a molecule or an aziridine type. Further examples include ahydroxyl group-reactive type such as a melamine resin type of butyratedmelamine or full-etherified melamine, or an isocyanate type representedas an aqueous block isocyanate. Still further examples include acarbonyl group-reactive type such as a dihydrazide type.

[0098] In addition to these examples, there are illustrated anethyleneimine type having an active amino group such aspolyethyleneimine, aminoethyl-modified ethyleneimine oraziridinyl-modified ethyleneimine, an aliphatic amine such aspolymethylene diamine, an aromatic amine such as diaminodiphenylmethane,an epoxy resin type having a glycidyl ether structure, and an aqueousoligomer such as an acryl oligomer having a (meth)acryloyl group.Examples of the aqueous oligomer include an oligoester (meth)acrylatemainly having an ester bond, an epoxy (meth)acrylate having an epoxyresin as a main structure, and the like.

[0099] They are used respective alone or in a mixture of two or more.

[0100] Among them, a carboxyl group-reactive type is particularlypreferable since it is excellent in dispersibility in a pigmentdispersion.

[0101] A blending ratio of a crosslinking agent to a resin is preferably1/100-50/100 at a weight ratio (crosslinking agent/resin (effectivesolid content weight ratio)). If the weight ratio is smaller than 1/100,a crosslinking effect becomes poor and stability of a dispersion or anink becomes poor, and if the weight ratio is larger than 50/100,agglomeration of pigments tends to occur and a viscosity of the liquidbecomes high.

[0102] In order to make the crosslinking reaction fully proceed, theweight ratio should be at least 1/100, preferably at least 2/100, and inorder to prevent qualities of an aqueous pigment dispersion fromlowering due to an excess amount of a crosslinking agent, the weightratio is at most 50/100, preferably at most 45/100, and any furtherimprovement of the crosslinking effect can not be expected if the weightratio is still larger.

[0103] Also, it is possible to cause crosslinking without a crosslinkingagent. In such a case, a combination of at least two kinds ofcrosslinkable functional groups must be contained in a molecule.

[0104] Examples of a self-crosslinkable functional group include aradical-polymerizable unsaturated functional group and a hydrolyzablealkoxysilane group.

[0105] Examples of a combination of such radical-polyemerizableunsaturated functional groups include preferably a combination of acarboxyl group and an epoxy group, a combination of a carboxyl group anda 1,3-dioxolan-2-on-4-yl group, a combination of a hydroxyl group and ablocked isocyanate group, a combination of a hydroxyl group and aN-alkoxymethylamide group, a combination of a hydroxyl group and ahydrolyzable alkoxysilane group or a combination of an amino group andan epoxy group, and a self-crosslinkable functional group may beintroduced when copolymerizing the above-mentioned hydrophobic monomerand hydrophilic monomer.

[0106] Temperature and time for crosslinking a resin are not speciallylimited, and may be adjusted depending on kinds of a resin and acrosslinking agent employed.

[0107] pH at the time of finishing the crosslinking reaction may be in arange of from 7.0 to 10.0, and if pH is at most 7.0, there is apossibility that a water-soluble resin dissolved by naturalization tendsto precipitate, and stability as a lapse of time becomes poor.

[0108] Depending on a crosslinking reaction, there are a case ofinitiating a curing reaction of a functional group at the same time assplashing water, a solvent and an organic amine under heating conditionand a case of causing polymerization-curing by an organic amine workingas a radical-generating source. In any case, tridimensional crosslinkingproceeds to form a film firmly bonded to a pigment, thereby improvingdispersion stability, and by producing a higher molecular material,gloss is improved.

[0109] The crosslinking treatment achieves remarkable effects of notcausing agglomeration and adsorption among pigment particles in water,maintaining a function of a resin itself as a dispersant, curing andstabilizing. Accordingly, it is preferable to maintain a functionalgroup, e.g. a polar group such as a carboxyl group, necessary formaintaining a resin itself in a dissolved state without completelyreacting the functional group in a resin, even after crosslinking

[0110] By carrying out such a crosslinking step of resin afterdispersing a pigment with the resin, a dispersing effect becomes higherand an aqueous pigment dispersion having a small particle size excellentin stability as a lapse of time can be obtained, as compared with a caseof dispersing a pigment with a previously crosslinked resin.

[0111] As a method for fixing a resin to the surroundings of a pigment,there is known a method of employing a precipitation reaction with apoor solvent, but the present method of combining a dispersing step anda crosslinking step has a merit of easily producing fine particles.

[0112] (Gel Fraction)

[0113] A crosslinking rate of a resin in a dispersion, i.e. so-called agel fraction, is preferably from 20 to 100%. In order to achieve suchphysical properties as alkali resistance and solvent resistance, the gelfraction is preferably at least 30%, more preferably at least 35%. Theupper limit of the gel fraction is 100%, and a higher gel fraction ismore preferable.

[0114] The gel fraction is generally considered as a measure of acrosslinking degree of a resin, but the gel fraction in the presentinvention is calculated from a numerical value determined by measuringan elution amount of a resin by drying an aqueous pigment dispersion topowder and using tetrahydrofuran as a solvent.

[0115] For example, an aqueous pigment dispersion is freeze-dried and 10g of the obtained powder is placed in 100 ml of tetrahydrofuran and isstirred at 60° C. for 1 hour. A gel fraction is calculated by measuringa solid content of a resin amount eluted in tetrahydrofuran and makingan elution amount at the time of not crosslinking as “blank”.

Gel fraction=(blank elution amount−elution amount after crosslinkingtreatment)/blank elution amount

[0116] Also, a weight average molecular weight of a crosslinked resin ispreferably at least 30,000, more preferably at least 200,000, in respectof fully improving properties of an aimed aqueous pigment dispersion. Alarger weight average molecular weight is more preferable.

[0117] Thus, by crosslinking a resin, a dispersion containing a pigmentand a crosslinked resin is obtained.

[0118] It is preferable to improve stability as a lapse of time byadjusting pH of the dispersion containing a crosslinked resin to thealkali side. It is preferable to adjust to pH of at least 8, morepreferably pH of 8.5-10.

[0119] (With Regard to Ion Exchange)

[0120] It is preferable to adjust a divalent metal ion content in anaqueous pigment dispersion to at most 100 ppm by treating with an ionexchange resin or the like. It is more preferable to adjust to 50 ppm.

[0121] It is possible to use a weak acidic cation exchange resin, astrong acidic cation exchange resin or the like as a cation exchangeresin. A well known ion exchange resin is usable, and it is possible touse a commercially available ion exchange resin.

[0122] Contact of a dispersion and an ion exchange resin is effected bya method of passing a dispersion through an ion exchange-treating toweror column apparatus, or a method of simply mechanically mixing andstirring a dispersion and an ion exchange resin, or other optionalmethods. A metal ion content can be measured by an atomic absorptionphotometer Z-8230 (Hitachi, Ltd.) or an ICP analyzing apparatus SPQ9000(Seiko Denshi Corporation), and the numerical values in the presentinvention were measured by these apparatuses.

[0123] By reducing a multi-valent metal ion content considered to causeagglomeration, stability of a recording ink as a lapse of time can beachieved, and by preventing agglomeration of an organic pigment, aviscosity increase of a recording ink can be controlled, therebyimproving an injecting property of recording ink. A multi-valent ioncontent in a recording ink is preferably at most 100 ppm, morepreferably at most 80 ppm.

[0124] One of methods of removing multi-valent metal ions is to treat adispersion or a recording ink with a cation exchange resin. The cationexchange resin (weak acidic cation exchange resin, strong acidic cationexchange resin) used is not specially limited so long as it removes amulti-valent metal ion, and a commercially available cation exchangeresin may be appropriately selected. Examples of the commerciallyavailable cation exchange resin include ┌DIAION WK 10┘, ┌DIAION WK 11┘,┌DIAION WK 20┘, ┌DIAION PA 406┘, ┌DIAION PA 408┘, ┌DIAION PA 412┘,┌DIAION PA 416┘, ┌DIAION PA 418┘, ┌DIAION PK 208┘, ┌DIAION PK 212┘,┌DIAION PK 216┘, ┌DIAION PK 220┘ and ┌DIAION PK 228┘ (manufactured byMitsubishi Chemical Corporation), ┌Amberlite IR-118H┘, ┌AmberliteIR-120B┘, ┌Amberlite IR-122┘, ┌Amberlite IR-124┘, ┌Amberlite 252┘,┌Amberlite 201CT┘, ┌Amberlite 200C┘, ┌Amberlite IRC-50┘ and ┌AmberliteIRC-84┘ (manufactured by Organo Corporation).

[0125] If necessary, the treatment may be carried out in combinationwith an anion exchange resin (weak basic anion exchange resin, mediumbasic anion exchange resin or strong basic anion exchange resin)treatment. Examples of the anion exchange resin include ┌DIAION WA 10┘,┌DIAION WA 11┘, ┌DIAION WA 20┘, ┌DIAION WA 21┘, ┌DIAION WA 30┘, ┌DIAIONPA 406┘, ┌DIAION PA 408┘, ┌DIAION PA 412┘, ┌DIAION PA 416┘, ┌DIAION PA418┘, ┌DIAION PA 306┘, ┌DIAION PA 308┘, ┌DIAION PA 312┘, ┌DIAION PA316┘, ┌DIAION PA 318┘, ┌DIAION SA 10A┘, ┌DIAION SA 11A┘, ┌DIAION SA12A┘, ┌DIAION SA 20A┘ and ┌DIAION SA 21A┘ (manufactured by MitsubishiChemical Corporation), ┌Amberlite IRA-400T┘, ┌Amberlite IRA-430┘,┌Amberlite IRA-458┘, ┌Amberlite IRA-458┘, ┌Amberlite IRA-900┘,┌Amberlite IRA-904┘, ┌Amberlite IRA-938┘, ┌Amberlite IRA-958┘,┌Amberlite IRA-410┘, ┌Amberlite IRA-411┘, ┌Amberlite IRA-91┘, ┌AmberliteIRA-68┘, ┌Amberlite IRA-35┘ and ┌Amberlite IRA-93┘ (manufactured byOrgano Corporation).

[0126] (With Regard to Ultrafiltration)

[0127] As a method for removing impurities, an ultrafiltration membraneis used. Generally, this means a treatment with a separating membranecapable of removing each component from compounds having respectivelyfrom a low molecular weight to a high molecular weight and ionicmaterials in a solution by each kind of membranes.

[0128] Examples of impurities include a material remaining at the timeof preparing a pigment, an excess component in a dispersion liquidcomposition, a dispersant not adsorbed on an organic pigment, and acontaminating component.

[0129] A molecular weight of a material separatable by anultrafiltration membrane varies depending on its fractional molecularweight of the ultrafiltration membrane. For example, when a fractionalmolecular weight of the ultrafiltration membrane used in the treatmentis 1000, only a material having a molecular weight of at most 1000 isseparatable from a solvent.

[0130] (Pigment Dispersion Liquid)

[0131] The pigment dispersion liquid of the present invention contains adispersion medium in addition to the above-described pigment andspecific resins. The dispersion medium is not specially limited, and adispersion medium conventionally used for a pigment dispersion liquidcan be selected. For example, water and other aqueous medium arepreferable, but other various organic solvents may be contained. Theaqueous medium used herein means water or a water-soluble solventcompatible with water. It is particularly preferable to use anion-exchanged water as water, but it is not limited thereto. Awater-soluble solvent is preferably selected from solvents used in anink composition described below.

[0132] Other components in the pigment dispersion liquid are notspecially limited and optimally selected so long as they do notadversely affect physical properties of the dispersion or do notadversely affect the preparation of an ink, and may include a solventselected from an organic solvent used in an ink composition for ink jetdescribed below or an additive such as a mildew-proofing agent to anaqueous ink composition using an aqueous medium.

[0133] (Ink Composition for Ink Jet)

[0134] The ink composition of the present invention is an inkcomposition for ink jet having a pigment dispersed, and is an inkcomposition for ink jet characterized by containing a water-solubleresin and a resin having a urethane bond and/or an amide bond.

[0135] The preparation method of the ink composition of the presentinvention is not specially limited, but it is preferable to prepare apigment dispersion liquid by the above-mentioned method and to removecoarse particles contained therein by centrifugal treatment, andthereafter it is preferable to proceed with an ink-producing step byadding an organic solvent such as a water-soluble organic solvent.

[0136] A content of a pigment in the ink composition is preferably atleast 0.5 wt %, more preferably at least 2 wt %, in order tosatisfactorily achieve a coloring effect, and is preferably at most 25wt %, more preferably at most 10 wt %, in order to provide anappropriate viscosity for maintaining a satisfactory injectingperformance at the viscosity of the ink composition.

[0137] Examples of a preferable water-soluble organic solvent includeethylene glycol, diethylene glycol, triethylene glycol, polyethyleneglycol, propylene glycol, butylene glycol, 1,2,6-hexanetriol,thioglycol, hexylene glycol, glycerin, diglycerin, 2-pyrrolidone,N-methyl-2-pyrrolidone, 1,5-pentanediol, 1,3-dimethyl-2-imidazolidinoneand the like, and they may be used respective alone or in a mixture oftwo or more.

[0138] The water-soluble organic solvent is added in an amount of from 5to 30 wt %, preferably from 6 to 25 wt %, to an ink liquid, and if thewater-soluble organic solvent is added in an amount of higher than theabove upper limit, the ink itself becomes highly viscous, andconsequently stability and injecting performance of the ink become poor,a blur into a paper becomes large, and a drying speed becomes low.Particularly, it is preferable that the viscosity is at most 20 mPa·s.

[0139] In addition to the above solvents, other water-soluble organicsolvents may be used, examples of which include methanol, ethanol,n-propanol, iso-propanol, n-butanol, iso-butanol, t-butanol,trimethylolpropane, ethylene glycol monoethyl ether, ethylene glycolmonobutyl ether, and the like.

[0140] Further, the ink composition of the present invention may containsuch additives as a mildew-proofing agent, a defoaming agent, arust-proofing agent, an antiseptic agent and the like.

[0141] As described above, the ink composition of the present inventionis excellent particularly as an ink for ink jet. For example, the inkcomposition is applicable to an ink jet recording method characterizedin that printing is carried out by injecting the ink composition througha nozzle of an ink jet printer or an ink jet recording methodcharacterized in that recording is carried out by liquid droplets formedby applying heat energy to the ink composition. Further, the inkcomposition of the present invention is applicable to an ink jetrecording method characterized in that recording is carried out byliquid droplets formed by applying a mechanical energy to the inkcomposition.

[0142] (With Regard to Preparation of High Permeability)

[0143] The ink composition of the present invention is particularlysuitable for being used as an ink jet ink having a high permeability.For example, conventionally known various methods can be employed forraising a high permeability. For instance, JP-A-2001-302,950 illustratesan ink composition having an improved permeability to a recording mediumand having an excellent continuous injecting stability by containing asurfactant having an acetylene bond. Also, it is possible to add apropylene oxide adduct of a lower alcohol.

[0144] Further, JP-A-2002-3760 illustrates one containing a compound ofthe following chemical formula (1) having an acetylene bond,1,5-pentanediol, and a butyl ether type solvent.

[0145] Further, JP-A-2002-30,237 illustrates an ink compositioncontaining an acetylene glycol type surfactant and/or a polysiloxanetype surfactant, an alkylether derivative of a polyhydric alcohol, thealkyl carbon number of which is at least 3 (preferably from 3 to 6), asan organic solvent, and/or 1,2-alkanediol, as a satisfactory inkcomposition having an excellent color reproducibility, a highpermeability and a short drying time.

[0146] As described in JP-A-2002-30,237, examples of an organic solventinclude ethylene glycol monobutyl ether, diethylene glycol mono-n-propylether, ethylene glycol monoethyl ether, ethylene glycol mono-iso-propylether, diethylene glycol mono-iso-propyl ether, ethylene glycolmono-n-propyl ether, ethylene glycol mono-t-butyl ether, diethyleneglycol mono-n-butyl ether, triethylene glycol mono-n-butyl ether,diethylene glycol mono-t-butyl ether, 1-methyl-1-methoxybutanol,propylene glycol mono-t-butyl ether, propylene glycol mono-n-propylether, propylene glycol mono-iso-propyl ether, propylene glycolmono-n-butyl ether, dipropylene glycol mono-n-butyl ether, dipropyleneglycol mono-n-propyl ether, dipropylene glycol mono-iso-propyl ether,and the like.

[0147] As described in JP-A-2002-30,237, examples of a 1,2-alkanediolinclude preferably 1,2-C₁C₈ alkanediol, more preferably 1,2-C₁C₆alkanediol, most preferably 1,2-hexanediol. The 1,2-alkanediol is addedin an amount of from 1 to 15 wt %, preferably 2 to 10 wt %.

[0148] Preferable examples of an acetylene glycol type surfactantinclude various compounds illustrated in JP-A-2002-30237. Moreparticular examples include Surfynol 82, 104, 440, 465, 485, TG(manufactured by Air Products and Chemicals, Inc.), Orfin STG, E1010(manufactured by Nisshin Kagaku K.K.), and the like.

EXAMPLES

[0149] The present invention is further illustrated with reference tothe following Examples. In the Examples, “part” means “part by weight”,and “%” means “wt %”.

Example 1

[0150] The following respective components were charged into a pressurekneader, and were kneaded at room temperature for 10 hours to prepare apigment kneaded product. (P.R122 (C.I. 73915) 100.0Styrene-methylstyrene-acrylic acid copolymer 20.0 (acid value 200,weight average molecular weight 7500, glass transition temperature 80°C.) Glycerin 67.0 Isopropyl alcohol 20.0

[0151] Thereafter, 42 parts of the above obtained pigment kneadedproduct, 3 parts of triethanolamine and 55 parts of ion-exchanged waterwere mixed, and were stirred under heating at 95° C. for 2 hours, andwere subjected to 3 pass treatment using 0.5 mm glass beads in a sandmill to prepare a dispersion liquid.

[0152] The dispersion liquid was adjusted to pH 8.5 with sodiumhydroxide, and was subjected to centrifugal treatment at 25000 G for 5minutes to remove coarse particles. After removing the coarse particles,the dispersion liquid had a solid content of 26.0%, a pH value of 8.3and a pigment particle size (volume 50% dispersion size) of 75.2 nm.

[0153] 10.0 Parts of a polyester type polyurethane resin (acid value 20,triethylamine neutralization, solid content 35%) and 5 parts of a 30%polycarbodiimide type crosslinking agent (carbodiimide equivalent 300,completely water-soluble) were added to the dispersion liquid, and theresultant mixture was stirred at 90° C. for 5 hours to crosslink theresin in the dispersion liquid. At the time of finishing thecrosslinking reaction, pH was 7.4. Gel fraction exceeded 35%. Further,solid content concentration was adjusted to 20 wt %. The dispersionliquid thus prepared is referred to as “magenta dispersion”. An inkcomposition was prepared by using the magenta dispersion thus obtainedand the following components. Component Amount (parts) Magentadispersion (solid content 20%) 15.0 Diethylene glycol 15.0Diethyleneglycol mono-n-propyl ether 10.0 Glycerin 4.0 Orfin STG 1.0Antiseptic agent (benzisothiazoline) 0.2 Ion exchanged water 54.8

[0154] The above components were stirred for 30 minutes to form an inkcomposition.

[0155] (Evaluation Test)

[0156] The above obtained composition was tested to evaluate stabilityas a lapse of time and injecting performance in accordance with thefollowing methods, and the results are shown in the following Table 1.

[0157] (a) Test for Stability as A Lapse of Time

[0158] The ink composition was allowed to stand in a constanttemperature room at 50° C. for 1 month, and presence or absence ofseparation of pigment, water floating and precipitation as well aschanges in viscosity and average particle size of pigment were observed.It was evaluated as “abnormal” when the separation of pigment, waterfloating and precipitation occurred even at a small degree or thechanges in viscosity and average particle size of pigment were caused.

[0159] As this result, normal state was expressed as “◯”, and abnormalstate was expressed as “X”

[0160] (b) Test for Injecting Performance

[0161] The ink composition charged into a cartridge, and 200 papersheets were printed at 2880×1440 dpi (4 pl) by using a printer“PM-4000PX” (manufactured by Seiko Epson Corporation). The paper sheetused was PM photographic paper<gloss> (manufactured by Seiko EpsonCorporation). It was evaluated as “abnormal” when clogging of a nozzleor unsatisfactory printing was caused even at a small degree.

[0162] Normal state was expressed as “◯”, and abnormal state wasexpressed as X

[0163] (c) Gloss

[0164] The paper sheet printed by the above injecting performance test(b) was measured with regard to gloss on 200 mirror surface by using agloss meter VG2000 (manufactured by Nippon Denshoku Kogyo K.K.).

[0165] (d) Friction Resistance

[0166] The above printed paper sheet was rubbed with a hand to evaluatefriction resistance. The results were expressed as “◯” (excellent), “Δ”(acceptable) and “X” (unacceptable), and are shown in the followingTable 1.

Comparative Example 1

[0167] An ink composition was prepared in the same manner as in Example1, except that the polyester type polyurethane resin was not added. Thesame evaluation tests as in Example 1 were carried out, and the resultsare shown in the following Table 1.

Example 2

[0168] The following respective components were charged into a pressurekneader, and were kneaded at room temperature for 8 hours to prepare apigment kneaded product. (P.Y14 (C.I. 21095) 100.0Styrene-methylstyrene-acrylic acid copolymer 20.0 (acid value 160,weight average molecular weight 8000, glass transition temperature 75°C.) Glycerin 67.0 Isopropyl alcohol 20.0

[0169] Thereafter, 42 parts of the above obtained pigment kneadedproduct, 1.5 parts of KOH and 56.5 parts of ion-exchanged water weremixed, and were stirred under heating at 80° C. for 2 hours, and weresubjected to 3 pass treatment using 0.5 mm glass beads in a sand mill toprepare a dispersion liquid.

[0170] The dispersion liquid was adjusted to pH 8.5 with sodiumhydroxide, and was subjected to centrifugal treatment at 25000 G for 5minutes to remove coarse particles. After removing the coarse particles,the dispersion liquid had a solid content of 26.8%, a pH value of 8.4and a pigment particle size (volume 50% dispersion size) of 9.8 nm.

[0171] 4 Parts of a polycarbonate type polyurethane resin (acid value30, triethylamine neutralization, solid content 40%) and 2 parts of a30% polyethyleneimine type crosslinking agent (amine hydrogen equivalent650, completely water-soluble) were added to the dispersion liquid, andthe resultant mixture was stirred at 90° C. for 3.5 hours to crosslinkthe resin in the dispersion liquid.

[0172] At the time of finishing the crosslinking reaction, pH was 7.8.Gel fraction exceeded 35%. Further, solid content concentration wasadjusted to 20 wt %. The dispersion liquid thus prepared is referred toas “yellow dispersion”. An ink composition was prepared by using theyellow dispersion thus obtained and the following components. ComponentAmount (parts) Yellow dispersion (solid content 20%) 15.0 Diethyleneglycol 10.0 Ethylene glycol monobutyl ether 10.0 Glycerin 7.0 Surfynol485 0.5 Antiseptic agent (benzisothiazoline) 0.2 Ion exchanged water57.3

[0173] The above components were stirred for 30 minutes to form an inkcomposition. The evaluation test was carried out in the same manner asin Example 1, and the results are shown in the following Table 1.

Example 3

[0174] The following respective components were charged into a pressurekneader, and were kneaded at room temperature for 8 hours to prepare apigment kneaded product. (Pigment.Blue 15:3 (C.I. 74160) 100.0Styrene-acrylic acid copolymer 20.0 (acid value 75, weight averagemolecular weight 12000, glass transition temperature 70° C.) Glycerin67.0 Isopropyl alcohol 20.0

[0175] Thereafter, 42 parts of the above obtained pigment kneadedproduct, 3.5 parts of triethanolamine and 54.5 parts of ion-exchangedwater were mixed, and were stirred under heating at 80° C. for 2 hours,and were subjected to 3 pass treatment using 0.5 mm glass beads in asand mill to prepare a dispersion liquid.

[0176] The dispersion liquid was adjusted to pH 8.5 with sodiumhydroxide, and was subjected to centrifugal treatment at 25000 G for 5minutes to remove coarse particles. After removing the coarse particles,the dispersion liquid had a solid content of 25.9%, a pH value of 8.3and a pigment particle size (volume 50% dispersion size) of 56.3 nm.

[0177] 40 Parts of a polyether type polyurethane resin (acid value 50,triethylamine neutralization, solid content 25%) and 8 parts of a 20%epoxy resin (epoxy equivalent 200) were added to the dispersion liquid,and the resultant mixture was stirred at 90° C. for 5 hours to crosslinkthe dispersed resin in the dispersion liquid.

[0178] At the time of finishing the crosslinking reaction, pH was 7.8.Gel fraction exceeded 35%.

[0179] Further, solid content concentration was adjusted to 20 wt %. Thedispersion liquid thus prepared is referred to as “blue dispersion”. Anink composition was prepared by using the blue dispersion thus obtainedand the following components. Component Amount (parts) Blue dispersion(solid content 20%) 15.0 Ethylene glycol monoethyl ether 10.02-Pyrrolidone 5.0 1,2-Hexanediol 10.0 Surfynol 465 0.5 Antiseptic agent(benzisothiazoline) 0.2 Ion exchanged water 59.3

[0180] The above components were stirred for 30 minutes to form an inkcomposition. The evaluation test was carried out in the same manner asin Example 1, and the results are shown in the following Table 1.

Example 4

[0181] The following respective components were charged into a pressurekneader, and were kneaded at room temperature for 12 hours to prepare apigment kneaded product. (Pigment.Green 7 (C.I. 74260) 100.0 Ethylmethacrylate-methacrylic acid copolymer 20.0 (acid value 120, weightaverage molecular weight 15000, glass transition temperature 65° C.)Glycerin 67.0 Isopropyl alcohol 20.0

[0182] Thereafter, 42 parts of the above obtained pigment kneadedproduct, 2.5 parts of triethanolamine and 55.5 parts of ion-exchangedwater were mixed, and were stirred under heating at 80° C. for 2 hours,and were subjected to 3 pass treatment using 0.5 mm glass beads in asand mill to prepare a dispersion liquid.

[0183] The dispersion liquid was adjusted to pH 8.5 with sodiumhydroxide, and was subjected to centrifugal treatment at 25000 G for 5minutes to remove coarse particles. After removing the coarse particles,the dispersion liquid had a solid content of 25.5%, a pH value of 8.4and a pigment particle size (volume 50% dispersion size) of 81.1 nm.

[0184] 4 Parts of a polycarbonate type polyurethane resin (acid value30, triethylamine neutralization, solid content 40%) and 2 parts of a30% polyethyleneimine type crosslinking agent (amine hydrogen equivalent650, completely water-soluble) were added to the dispersion liquid, andthe resultant mixture was stirred at 90° C. for 2.5 hours to crosslinkthe resin in the dispersion liquid.

[0185] At the time of finishing the crosslinking reaction, pH was 7.6.Gel fraction exceeded 35%. Further, solid content concentration wasadjusted to 20 wt %. The dispersion liquid thus prepared is referred toas “green dispersion”. An ink composition was prepared by using thegreen dispersion thus obtained and the following components. ComponentAmount (parts) Green dispersion (solid content 20%) 15.0 Propyleneglycol mono-n-butyl ether 15.0 2-Pyrrolidone 10.0 Isopropanol 3.0 OrfinSTG 0.5 Antiseptic agent (benzisothiazoline) 0.2 Ion exchanged water56.3

[0186] The above components were stirred for 30 minutes to form an inkcomposition.

Comparative Example 2

[0187] The following respective components were charged into a pressurekneader, and were kneaded at room temperature for 8 hours to prepare apigment kneaded product.

[0188] An ink composition was prepared in the same manner as in Example4, except that the polycarbonate type polyurethane resin was not added.The same evaluation tests as in Example 1 were carried out, and theresults are shown in the following Table 1.

Example 5

[0189] (Pigment.Red 22 (C.I. 12315) 100.0 Styrene-maleic acid copolymer20.0 (acid value 180, weight average molecular weight 3000, glasstransition temperature 65° C.) Glycerin 67.0 Isopropyl alcohol 20.0

[0190] Thereafter, 42 parts of the above obtained pigment kneadedproduct, 3.0 parts of triethanolamine and 55.0 parts of ion-exchangedwater were mixed, and were stirred under heating at 85° C. for 2 hours,and were subjected to 3 pass treatment using 0.5 mm glass beads in asand mill to prepare a dispersion liquid.

[0191] The dispersion liquid was adjusted to pH 8.5 with sodiumhydroxide, and was subjected to centrifugal treatment at 25000 G for 5minutes to remove coarse particles. After removing the coarse particles,the dispersion liquid had a solid content of 26.0%, a pH value of 8.4and a pigment particle size (volume 50% dispersion size) of 64.8 nm.

[0192] 5 Parts of a polyether type polyurethane resin (acid value 50,triethylamine neutralization, solid content 40%) and 1 part of a 35%oxazoline type crosslinking agent (oxazoline equivalent 200) were addedto the dispersion liquid, and the resultant mixture was stirred at 80°C. for 2.5 hours to crosslink the resin in the dispersion liquid.

[0193] At the time of finishing the crosslinking reaction, pH was 7.5.Gel fraction exceeded 35%. Further, solid content concentration wasadjusted to 20 wt %. The dispersion liquid thus prepared is referred toas “red dispersion”. An ink composition was prepared by using the reddispersion thus obtained and the following components. Component Amount(parts) Red dispersion (solid content 20%) 15.0 Ethylene glycol 15.0Triethylene glycol monobutyl ether 10. 0 Isopropanol 1.0 Surfynol 4850.7 Antiseptic agent (benzisothiazoline) 0.2 Ion exchanged water 58.1

[0194] The above components were stirred for 30 minutes to form an inkcomposition.

Example 6

[0195] An ink composition was prepared in the same manner as in Example2, except that the polycarbodiimide type crosslinking agent was notadded. The same evaluation tests as in Example 1 were carried out, andthe results are shown in the following Table 1.

Example 7

[0196] An ink composition was prepared in the same manner as in Example3, except that the kneading step was not carried out. The sameevaluation tests as in Example 1 were carried out, and the results areshown in the following Table 1.

Example 8

[0197] An ink composition was prepared in the same manner as in Example5, except that the centrifugal treatment of removing coarse particleswas not carried out. The same evaluation tests as in Example 1 werecarried out, and the results are shown in the following Table 1. TABLE 1Stability as a Injecting Gloss Friction lapse of time performance valueresistance Example 1 ◯ ◯ 61.1 ◯ Example 2 ◯ ◯ 78.5 ◯ Example 3 ◯ ◯ 58.6◯ Example 4 ◯ ◯ 54.3 ◯ Example 5 ◯ ◯ 63.9 ◯ Example 6 X ◯ 77.9 Δ Example7 ◯ ◯ 41.2 Δ Example 8 ◯ X 36.8 Δ Comp. Ex. 1 X ◯ 49.6 X Comp. Ex. 2 X ◯47.3 X

[0198] As evident from the above results, such a pigment dispersion forink jet having a pigment dispersed as an aqueous pigment dispersion,characterized by containing a water-soluble resin and a resin having aurethane bond and/or an amide bond, and an ink composition using thesame, are greatly improved in stability in a highly permeable solvent,and have excellent friction resistance and gloss.

INDUSTRIAL APPLICABILITY

[0199] The present invention can provide a pigment dispersion for inkjet and an ink composition for ink jet, which are greatly improved instability in a highly permeable solvent and have excellent frictionresistance and gloss.

1. A pigment dispersion for ink jet having a pigment dispersed, whichcomprises a water-soluble resin and a resin having a urethane bondand/or an amide bond.
 2. The pigment dispersion according to claim 1,which is obtained by blending the water-soluble resin with the pigment,finely pulverizing the pigment in a kneading step and a dispersing step,and further adding the resin having a urethane bond and/or an amide bondthereto to cause crosslinking.
 3. The pigment dispersion according toclaim 1 or 2, wherein the resin has a crosslinking rate of from 20 to100%.
 4. The pigment dispersion according to any one of claims 1 to 3,which is a dispersion for ink jet.
 5. An ink composition for ink jethaving a pigment dispersed, which comprises a water-soluble resin and aresin having a urethane bond and/or an amide bond.
 6. The inkcomposition for ink jet according to claim 5, which is obtained byblending the water-soluble resin with the pigment, finely pulverizingthe pigment in a kneading step and a dispersing step, and further addingthe resin having a urethane bond and/or an amide bond thereto to causecrosslinking.
 7. The ink composition for ink jet according to claim 5 or6, wherein the resin has a crosslinking rate of from 20 to 100%.
 8. Anink composition for ink jet, which is obtained by adding an organicsolvent to the pigment dispersion as defined in any one of claims 1 to3.
 9. An ink jet recording method, which comprises printing bydischarging the ink composition for ink jet as defined in any one ofclaims 5 to 8 from a nozzle of an ink jet printer.
 10. An ink set havingthe ink composition for ink jet as defined in any one of claims 5 to 8charged into a cartridge.